Greenhouse shade advice needed.

[K-Sci]

Is 20% shade (light diffusing glass) enough at this time of year with peak ambient greenhouse interior temperatures in the low 90Fs and gentle air movement. I'm thinking of removing my 40% shade cloth, which in combination with the 20% light reduction of the light-diffusing glass puts the current shading combined at 48% of full sun. Is a 48% to 80% change likely to cause leaves to burn?



-Keith

[estación seca]

If the air circulation is high it won't be a problem. Moving air carries the heat from leaves and allows them to stay at ambient temperatures.

High air circulation means everything is moving.

[K-Sci]

Originally Posted by estación seca

If the air circulation is high it won't be a problem. Moving air carries the heat from leaves and allows them to stay at ambient temperatures.

High air circulation means everything is moving.

I have been trying not to get everything moving because I end up needing to water some plants more than once per day. I was already thinking I could aim the two ceiling-mounted circulation fans that blow above the plants slightly downward and leave my big floor fan on for more than only after bi-weekly watering. That would definitely move everything, so with your input. I will try it this weekend when I'm home - if it is sunny and hot.

Most of my orchid growing has been in either indoors or in moderate maritime coastal climates like San Diego, Seattle Washington and Brunswick Maine. Last fall when it got cool, I grew my Neofinetias outdoors on a table in full sun. I've been afraid to remove the shade cloth in the hot Mississippi summer because burned a few Phalaenopsis the first two years I was here in the spring giving them only early morning sun. Now, with the greenhouse, I could burn thousands of dollars of orchids in a day.

-Keith

---------- Post added at 06:54 PM ---------- Previous post was at 06:47 PM ----------

Originally Posted by Ray

Keith, FWIW, orchid greenhouses I am familiar with in full sun in PA (Parkside) - with less solar intensity - typically had two layers of 30% in summer and one in winter. My greenhouse was partially shaded by a hillside and trees, so I went with 30% in summer and none in winter.

Parkside’s cover was 6-mil PE x 2, mine was 8 mm polycarbonate, and I don’t know how much intensity reduction your diffusing cover provides.

Ray, that's really great input. My greenhouse is an east-south-east facing lean-to. It is shaded from around 2:00-3:00 on by a sloped roof during the hottest part of the day. With 20% shade diffusing panels overhead, I may be okay, so long as I start with a lot of air movement and remove the shade cloth by sliding it up a couple feet in stages over a couple weeks.



-Keith

---------- Post added at 06:56 PM ---------- Previous post was at 06:54 PM ----------

Originally Posted by isurus79

That's a major shade reduction when the sun is still strong and the temps are still high. My guess is that the plants would be fine with less shade but not at that quick of a reduction this time of year.

My thoughts exactly. Better to err on the safe side. If I do it gradually the weather will be cooler by the time it is off too.

-Keith

[K-Sci]

Originally Posted by estación seca

If the air circulation is high it won't be a problem. Moving air carries the heat from leaves and allows them to stay at ambient temperatures.

High air circulation means everything is moving.

I cut down a tall shrub at the south end of my greenhouse not realizing that the sun is low enough to shine on the first 3 feet of bench. As a result, the plants there get very strong sunlight (6000fc) with daytime highs in the mid 80's. My C. tigrina, C. walkeriana, and Neofinetia falcata are receiving these high light levels for 4-5 hours/day. With strong air movement the leaves get comfortable bathwater warm. I see no burning or yellowing from the heat.

Oddly, our weather has been crazy lately here in S. central Mississippi. Tomorrow our forecast is 88F high/ 55F low - that's a 33F day-night swing. It's been like that for the last 4 nights. A 20F swing is pretty typical. The orchids only see about a 25F of the 33F swing because I button up the greenhouse at night. I don't want the phalaenopsis, in particular, to be chilled below 55-60F.

-Keith

[Shadeflower]

Interesting discussion guys. Hope to hear how these light adjutments go.

I am still forming my own clonclusions and haven't been growing catts long enough yet but my early conclusions go a long these lines.

Too much light can cause burns in the leaves
Too much heat can cause sunburns (similar to the above basically but more damage)

Too much light can also cause leaf bleaching where the ends turn too yellow and too much light can cause leaves to redden.

I am planning to perform my own experiemtns. I've got one that is developing some leaf bleaching from too much light but the leaves are actively seeking out the light and the leaves have not got any sunburn.

So I could turn down the light but based on my recent discussion on fertilizing I am planning to experiement by providing this one a bit more fertilizer. I am a bit anxious doing it, I have doubled my fertilizer strength which has doubled the Nitrogen so wish me luck. I hope it works out ok.

I also have a Vanda, a Cattleya and a Dendrobium which I moved to higher light. The change in growth in the Dendrobium was phenomental. It went from doing nothing to produing 5 new bulbs but at the same time those bulbs grew a bit stunted and had very red leaves. Too much light right? No. I really do not believe so. The change in growth the increased light triggered was amazing but at the same time producing 5 bulbs just overwhelmed this plant which had very low energy reserves (wrinkled bulbs) so all the leaves turned red.

I could move the plant to a lower light but I believe that is not the full story. So red leaves are generally caused by a phosphorous or magnesium deficiency. Like said I am fully aware that the more light you give the worse the problem gets but I don't think the plant is getting too much light as it hasn't gotten sunburns yet which even more light would cause. But trying to grow faster under higher light triggers the deficiency (if there is one) to get worse so it's time for me to test this out so I'll be giving one more phosphorous, a couple more Magnesium and the one with bleached leaves will get more Nitrogen,

Then the phalaenopsis I have with red leaves, like Tedro's, I will also be experimenting with after reading that phalaenopsis need twice the N than Cattleya's do.

Shold be interesting. Eager to hear opinions or suggestions but I have a limited number of plants to try this with so we'll see what I find.

Again one can always lower light but that at the same time would surely lower flowering.

I don't believe in the concept that lowering light improves flowering for some. I've seen it suggested. I don't believe it and think there is more to it.

So we shall see, I will make some observations and hopefully know more by next year.

[K-Sci]

Originally Posted by Shadeflower

Hope to hear how these light adjutments go...I am still forming my own clonclusions.

Discussing light levels is a bit loose-goosey when the actual light levels are not known. I use this light meter, which is very reasonably priced.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

What fertilizer brand/formulation are you using?

-Keith

[isurus79]

Originally Posted by Shadeflower

So red leaves are generally caused by a phosphorous or magnesium deficiency. Like said I am fully aware that the more light you give the worse the problem gets...

Not quite! Red leaves are the plant's natural sunscreen and are not a deficiency, nor are red leaves considered a problem.

[K-Sci]

Originally Posted by isurus79

Not quite! Red leaves are the plant's natural sunscreen and are not a deficiency, nor are red leaves considered a problem.

I've also never heard of red leaves being caused by a deficiency. Where did you hear this?


-Keith

[Roberta]

Originally Posted by K-Sci

he heat.

Oddly, our weather has been crazy lately here in S. central Mississippi. Tomorrow our forecast is 88F high/ 55F low - that's a 33F day-night swing. It's been like that for the last 4 nights. A 20F swing is pretty typical.

Sounds like perfect Cymbidium weather...

[K-Sci]

Originally Posted by Roberta

Sounds like perfect Cymbidium weather...

I have three warm-tolerant cymbidiums, but I'd bet they would benefit from the large temperatures swings too. Maybe I should take them out of the greenhouse until it gets down into the 40s.

When I lived in California I grew standard cymbidiums I got at Santa Barbara Orchid Estates. At that time they had a much larger number of offerings than they do now. I've not grown warm-tolerant ones before this year, but genetically I think they are hybrids of both warm and cold growing types and would be stronger with cool nights.

-Keith